Field of the Invention
The present invention relates to a device for folding a sheet bundle formed by sheets that are sequentially carried out from an image forming device such as a copier or a printer and accumulated in a bundle and, more particularly, to a sheet processing device that performs pressing against a fold of a two-folded sheet bundle.
Description of the Related Art
There are widely known processing devices that align sheets carried out from an image forming device, bind them, and fold them into a booklet. Among them, some processing devices are configured to saddle-stitch the sheet bundle with a staple or an adhesive and fold the sheet bundle into a booklet.
Such a device performs folding for sheet bundle formed by about 20 to 30 sheets in half; however, there may be a case where the two-folded sheet bundle is unintentionally opened after being discharged from the device, degrading aligning property of the sheet bundle, which results in reduction in accumulation amount.
Thus, it is widely known that, after the folding, the two-folded sheet bundle is subjected to pressing from above and below the fold.
For example, Japanese Patent No. 4,217,640 discloses a device that moves along a fold of a two-folded sheet bundle while pinching/pressing the fold by means of rollers disposed above and below the fold. This device is also provided with a flattening roller that presses the fold from a front side thereof at a position slightly rearward of the pinching/pressing position of the upper and lower rollers. That is, in this device, the rollers that pinch/press the fold from thereabove and therebelow and flattening roller that presses the fold from the front side thereof are formed into one unit, and this unit is moved along the sheet folding direction. Thus, only a portion that is pinched by the rollers can be made flat, thereby reducing wrinkles and breaks of a portion other than the fold due to a difference in gripping force.
Further, as illustrated in detail in FIGS. 11 and 12, Japanese Patent No. 4,217,640 discloses, as a device of a second embodiment of the specification, a device in which a unit provided with a flattening roller that presses the fold from the front side thereof and pinching roller pairs that are arranged at front and rear of the flattening roller so as to pinch/press the fold from thereabove and therebelow moves along the sheet folding direction. A device of such a type moves from outside one end portion of the sheet bundle in its width direction toward inside and passes the other end portion thereof while pinching/press the fold by means of the pinching roller pairs to thereby flatten a back-folded portion.
Further, Jpn. Pat. Appln. Laid-Open Publication No. 2014-76903 discloses a processing device provided with a pair of pressing rollers that press a fold of a two-folded sheet bundle in a sheet width direction and a moving unit that reciprocates the pressing roller pair in the sheet width direction. Further, this processing device is configured to move the pressing roller pair between a position where they are separated away from each other and a position where they are brought into pressure contact with each other. Upon pressing the sheet bundle, the moving unit moves inward from an end portion in the sheet width direction with the pressing roller pair separated away from each other and then moves from the inside to one end portion of the sheet bundle while pressing the sheet bundle. After passing the one end portion, pressing by the pressing roller pair is released to separate the pressing roller pair away from each other. When moving again for pressing, the moving unit passes the one end position of the sheet bundle with the pressing roller pair separated away from each other and then moves from the inside to the other end portion of the sheet bundle while pressing the sheet bundle. In other words, the pressing against the fold of the sheet bundle is started from the inside in the sheet width direction to the one or the other end portion of the sheet bundle.
The above-described devices that perform pressing against the folded sheet bundle carried out from an image forming device or the like have the following problems, respectively.
In the device disclosed in Japanese Patent No. 4,217,640, the roller pair that is previously brought into a pressure contact state is moved along the fold, so that even if the roller pair is reciprocated many times, the roller pair presses the same position, that is, the folded positions are overlapped in a straight line, with the result that the folded sheet bundle may be opened after the pressing. Thus, an accumulating property and an aligning property of the folded sheet bundle cannot be effectively improved.
Also, in the device disclosed in Jpn. Pat. Appln. Laid-Open Publication No. 2014-76903, the pressing against the fold of the sheet bundle by means of the pressing roller pair is repetitively performed with the same pressing force, so that, as in the case of the device disclosed in Japanese Patent No. 4,217,640, the folded positions are overlapped in a straight line, with the result that the folded sheet bundle may be opened after the pressing. Thus, improvement of the accumulating property and aligning property of the folded sheet bundle is conventionally difficult to achieve.